130 



FOYE. 



It is gray in color and slightly vesicular. There are no pheno- 

 crysts distinct in the hand specimen. The general structure of the 

 ground-mass is pilotaxitic but near the vesicles it is hyalopilitic. The 

 rock is chiefly composed of a mat of small labradorite (AbssAne?) 

 needles with occasional phenocrysts of labradorite and rather rare 

 phenocrysts of augite. 



4. Olivine andesite from Ono Levu. The rocks of Ono Levu are 

 very similar to those of Ndoi. The andesite to be described was col- 

 lected from the outcrop of a flow, forming the summit of a flat hill at 

 the northwestern end of the island. 



The rock is slate-black to dark purple in color. It is massive and 

 porph^ritic, with phenocrysts of feldspar, 4 to 6 mm. in diameter, 

 forming 30 per cent of its mass. Augite phenocrysts of a like size 

 form 10 per cent of the rock. 



The feldspar crystals are frequently zoned but vary only slightly 

 in composition. They are a basic andesine, Ab57An43. The augite 

 phenocrysts are twinned on the front pinacoid. There are very few 

 olivine phenocrysts. 



The ground-mass has a hyalopilitic texture but there is little glass 

 present. Minute needles of feldspar form the larger part of its com- 

 position; magnetite is present. 



The absence of abundant olivine phenocrysts in the rock reveals 

 the fact that it is not very basic. This conclusion is borne out by the 

 following analysis: — 



Si02 52.08 



TiO. 1.40 



AI2O3 17.86 



FeoOa 2.22 



FeO 5 . 76 



MnO 0.10 



MgO 3.89 



CaO 8.20 



Na..() 3.67 



KoO 2.07 



H-.() 2.35 



PaOs ^36 



99.96 



Norm 



Orthoclase 12.23 



Albite 31.44 



Anorthite 25.85 



Diopside 9.98 



Hypersthene 11 . 16 



Olivine 0.17 



Magnetite 3 . 25 



Ihnenite 2.74 



Apatite 0.93 



97.75 



Water __2.35 



100 . 10 



Specific gravity at 20°C = 2.792. 



